Mobile data transmission and data services are constantly making progress, wherein such services provide various communication services, such as voice, video, packet data, messaging, broadcast, etc. In recent years, Long Term Evolution LTE™ has been specified, which uses the Evolved Universal Terrestrial Radio Access Network E-UTRAN as radio communication architecture.
According to this architecture, the use of small cells in addition to macro cells is being discussed, e.g. in 3GPP RAN for Release 12 (Rel-12). Such small cells have a more limited transmission range than macro cells. Thereby, two scenarios are considered. On the one hand, where a user equipment UE is in coverage of both the macro cell and the small cell simultaneously, and, on the other hand, where the UE is not in coverage of both the macro cell and the small cell simultaneously.
The scenario where small cell nodes are not deployed under the coverage of one or more overlaid E-UTRAN macro-cell layer(s) is also the target of the small cell enhancement considerations.
Additionally, the backward compatibility, i.e. the possibility for legacy (pre-Rel-12) UEs to access a small-cell node/carrier, is desirable for small cell deployments.
According to the specifications from 3GPP, it is required to support the legacy UE in the small cell system. In addition, the operator usually has already deployed large number of legacy (pre-Rel-12) eNBs for coverage purpose, when the operator plans to deploy small cell system for capacity enhancement.
Thus, it is required to support the mobility to small cell involving legacy UE/eNB (base station; evolved NodeB) for supporting a handover HO of an UE from a legacy eNB to a small cell, as well as a handover HO of a legacy UE from an enhanced eNB to a small cell.
However, there is no known method to support the mobility involving the pre-Rel-12 UE and pre-Rel-12 eNB.